does any body place PoP parts? We are running them through a regular process(paste place reflow) and we don't have good rates on these. Mostly we observe opens at the sides of the part. We are thinking to purchase a flux feeder, but I wanted to see what are your opinions. Regards, Emil

Opens are on the device to the PCB - mainly on the edges, that makes me think I get some kind of warping,but even if I bake parts and boards doesn't help. We also tried different reflow profiles - same results. I hear that some people use dip fluxers and other techniques to mount these and I expect to hear from them.

And digging a bit further, are the opens at the device level (all the solder on PWB pad, none on device pad) or at the PWB (similar to pillow defect?)

After answering that, I would start thinking about(in this order)paste print quality and consistency, PWB solderability, PWB dimensions, thickness, and how the parts are conveyed through the oven (mesh or edge rail), about oven length, profiling, etc...

If you still are considering these PoP opens a possible warpage issue I might be able to help. I work for a company that measures warpage during heating (Akrometrix). I'll try and send you a message with details. I would be curious to hear if this has been fixed. Sometimes warpage is at a problem source, but some other approaches as suggested in this thread can often be used to resolved the surface mount failure without addressing the warpage problem.